JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container"></div>

CSS

.container {
    position: absolute;
    top: 0;
    left: 0;
    width: 100px;
    height: 100px;
    background-color: red;
}

.container:before {
    content: "";
    position:absolute;
    top: 10px;
    left: 20px;
    width: 100px;
    height: 100px;
    background-color: yellow;
    z-index: -1;
}